Chimps, humans and notions of fairness

Apparently it is "Science Sunday" here at The Lead. But bear with us, this story too has a connection to faith. It turns out that one of the characteristics that distinguish humans from chimpanzees (our closest relative) is that we have inherent notions of fairness--and chimps do not.

In a recent experiment announced in Science, scientists at the Max Planck Institute found that chimpanzees act as economic maximizers, but humans do not. The Economist describes the experiment:

Economic theory has contrived a species it calls Homo economicus—a “rational maximiser” who grabs what he can for himself. But, curiously, he makes no appearance in the ultimatum game, a classic economics experiment.

In this game, two players, a proposer and a responder, divide a reward. It could be a cake. It could be cash. It could even be a bunch of grapes. The game is so named because the proposition is an ultimatum. The responder can either accept the division or reject it. If he rejects it, both players receive nothing.

Homo economicus would accept any division in which his share was not zero. But that is not what happens. Scores of studies have run the ultimatum game across cultures and ages. Universally, people reject any share lower than 20%—apparently to punish the greed of the proposer. People do not act like Homo economicus. Instead, they are the arbiters of fairness.

To find out if chimpanzees share this sense of fairness, Keith Jensen and his colleagues at the Max Planck Institute for Evolutionary Anthropology, in Leipzig, designed a way for chimps to play the ultimatum game. Their version started with a pair of trays far from the players' cages. Each tray had ten raisins divided in different ways between two pots—say eight and two, or five and five. One chimp was allotted the role of proposer. He could choose one of the trays, pulling it by way of a rope just halfway to the cage. The other, the responder, could then choose to pull on a rod, bringing the tray close enough for both to get the raisins, one pot for each. If the responder chose not to pull the tray closer within a minute, the offer was considered rejected, and the game concluded.

The result, which Dr Jensen reports in Science, is that chimps are simply rational maximisers—Pan economicus, if you like. Though proposers consistently chose the highest possible number of raisins for themselves, responders rarely rejected even the stingiest offers.

This is a telling outcome. A number of researchers in the field of human evolution think that a sense of fairness—and a willingness to punish the unfair even at some cost to oneself—is humanity's “killer app”. It is what allows large social groups to form. Without it, free-riders would ruin such groups, because playing fair would cease to have any value. Dr Jensen's previous experiments have shown that chimpanzees are willing to punish actual thieves. But his new data add weight to the theory that the more sophisticated idea of fair shares, which underpins collaborative behaviour, appeared in the hominid line only after the ancestors of the two species split from one another.

And another set of experiments using this same game ahve found a genetic basis for our sense of fairness:

As they write in the Proceedings of the National Academy of Sciences, Bjorn Wallace of the Stockholm School of Economics and his colleagues have shown this by playing the ultimatum game with twins. They used the classic trick of neutralising the effect of upbringing and exposing that of genetics by comparing identical twins (who share all their genes) with fraternal twins (who share half).

Each twin of a pair played the ultimatum game, both as proposer and as responder. Dr Wallace found, in the case of identical twins, a striking correlation between the average division that each member of a pair proposed and also between what they were willing to accept. In other words, their senses of what was fair were similar. No such correlations were seen in the behaviour of fraternal twins.

Besides showing that a sense of fairness has a genetic basis, this result also raises a question: why should the sense of what is fair be so variable? It may be that in a population of the fair, the unfair prosper while amongst the unfair, the fair are better off. The result would be an equilibrium in which various attitudes to fairness do just as well as each other. But why, exactly, that should be the case is a subject for another day's research project.

Read it all here. You can learn more about the chimp experiment here, and more about the twin experiment here.

Many Christian apologists--most notably C.S. Lewis (and more recently Francis Collins) have argued that our unique human innate sense of morality is itself evidence of the existence of God. Do these recent experiments suggest a biological explanation for this innate "moral law"?

Comments (1)

Wow, that seems like a GREAT reason to keep chimpanzees locked up in lab cages--so we can see how many raisins they'll choose!

Now I believe that some animal experimentation is necessary for saving lives, but I highly doubt these experiments fall into that category. My reaction to the lab results is a yawn and a "So what?" My reaction to the use of caged animals for this kind of rubbish is "Shame on you!"

Doug Curlin

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